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Multimedia Traffic Control with IP Multicast (IGMP)
More on IGMP Operation
Number of IP Multicast Addresses Allowed
The total of static multicast filters and IGMP multicast filters (addresses)
together can range from 389 to 420, depending on the current max-vlans setting
in the switch. If multiple VLANs are configured, then each filter is counted
once per VLAN in which it is used.
Table 12-1. Maximum Allowed Number of Multicast Filters
Max-VLANs
Setting
Maximum # of Multicast Filters
(Static and IGMP Combined)
1 (the minimum) 420
8 (the default) 413
32 or higher 389
IGMP Operates With or Without IP Addressing
You can configure IGMP on VLANs that do not have IP addressing. The benefit
of IGMP without IP addressing is a reduction in the number of IP addresses
you have to use and configure. This can be significant in a network with a large
number of VLANs. The limitation on IGMP without IP addressing is that the
switch cannot become Querier on any VLANs for which it has no IP address—
so the network administrator must ensure that another IGMP device will act
as Querier and that an additional IGMP device is available as a backup Querier.
IGMP Function Available With IP Addressing
Configured on the VLAN
Available
Without IP
Addressing?
Operating Differences Without an IP Address
Drop multicast group traffic for which there Yes None
have been no join requests from IGMP clients
connected to ports on the VLAN.
Forward multicast group traffic to any port on Yes None
the VLAN that has received a join request for
that multicast group.
Forward join requests (reports) to the Querier. Yes None
Configure individual ports in the VLAN to Auto Yes None
(the default)/Blocked, or Forward.
Configure IGMP traffic forwarding to normal or Yes None
high-priority forwarding.
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